Electrocardiographs (ECGs) with pacemaker detection capability are known in the art. Since the pacemaker pulse is generally a high frequency, large amplitude pulse, conventional ECGs with pacemaker detection capability typically detect the pacemaker pulse using hardware which compares the electrocardiogram signal to an amplitude threshold. Then, once the pacemaker pulse is detected, the portion of the electrocardiogram signal containing the pacemaker pulse and any artifacts such as overshoot and ringing associated with filtering of the pacemaker pulse are blanked (removed) from the electrocardiogram signal using gates and the like before the electrocardiogram signal is processed. The QRS detection portion of the ECG monitor is then notified that there was a pacemaker event at the blanked portion of the waveform. Unfortunately, removal of the pacemaker pulse and its artifacts often has the unintended result of removing any QRS complexes which occur during the same time window.
On the other hand, prior art ECG monitors which detect pacemaker pulses but do not blank (remove) the artifacts associated with each pacemaker pulse before it enters any filtering process may cause QRS complexes to be falsely detected if the patient's heart does not respond to the pacemaker. Also, since QRS detectors are allowed by regulatory standards to detect signals as small as 0.15 mV, the artifacts following a pacemaker pulse can be large enough to be counted as a heart beat under some circumstances. This result is obviously undesirable.
Many prior art ECG monitors accomplish these pacemaker detection and rejection tasks using specially designed circuitry. Unfortunately, such systems are typically quite costly and relatively inflexible. Other ECG monitors typically determine the extent of the pacemaker artifact using a hardware detection circuit and then blank out a region following the pacemaker pulses using a software routine so that the artifacts following the pacemaker pulses do not falsely trigger the QRS detection portion of the ECG monitor. The period of time that must be blanked is determined by the hardware filter characteristics and can be quite long, for example, 45 ms. As in the prior art hardware embodiments, in addition to removing the artifact from the signal going to the QRS detector, the users are deprived of any information in the electrocardiogram signal (such as QRS complexes) which occur during the blanked interval.
Accordingly, it is desired to overcome these problems in the prior art by blanking only the pacemaker pulse and by adjusting the QRS detection operation so that pacemaker artifacts in a time window following detected pacemaker pulses do not cause false QRS complex detections. The present invention has been designed to meet these needs in the art.